Gene-knockout by iSTOP enables rapid reproductive disease modeling and phenotyping in germ cells of the founder generation

Cytosine base editing achieves C·G-to-T·A substitutions and can convert four codons(CAA/CAG/CGA/TGG)into STOP-codons(induction of STOP-codons,iSTOP)to knock out genes with reduced mosaicism.iSTOP enables direct phenotyping in founders’somatic cells,but it remains unknown whether this works in founders’germ cells so as to rapidly reveal novel genes for fertility.Here,we initially establish that iSTOP in mouse zygotes enables functional characterization of known genes in founders’germ cells:Cfap43-iSTOP male founders manifest expected sperm features resembling human“multiple morphological abnormalities of the flagella”syndrome(i.e.,MMAF-like features),while oocytes of Zp3-iSTOP female founders have no zona pellucida.We further illustrate iSTOP’s utility for dissecting the functions of unknown genes with Ccdc183,observing MMAF-like features and male infertility in Ccdc183-iSTOP founders,phenotypes concordant with those of Ccdc183-KO offspring.We ultimately establish that CCDC183 is essential for sperm morphogenesis through regulating the assembly of outer dynein arms and participating in the intra-flagellar transport.Our study demonstrates iSTOP as an efficient tool for direct reproductive disease modeling and phenotyping in germ cells of the founder generation,and rapidly reveals the essentiality of Ccdc183 in fertility,thus providing a time-saving approach for validating genetic defects(like nonsense mutations)for human infertility.

Coiled-coil domain-containing 38 is required for acrosome biogenesis and fibrous sheath assembly in mice

During spermiogenesis,haploid spermatids undergo dramatic morphological changes to form slender sperm flagella and cap-like acrosomes,which are required for successful fertilization.Severe deformities in flagella cause a male infertility syndrome,multiple morphological abnormalities of the flagella(MMAF),while acrosomal hypoplasia in some cases leads to sub-optimal embryonic developmental potential.However,evidence regarding the occurrence of acrosomal hypoplasia in MMAF is limited.Here,we report the generation of base-edited mice knocked out for coiled-coil domain-containing 38(Ccdc38)via inducing a nonsense mutation and find that the males are infertile.The Ccdc38-KO sperm display acrosomal hypoplasia and typical MMAF phenotypes.We find that the acrosomal membrane is loosely anchored to the nucleus and fibrous sheaths are disorganized in Ccdc38-KO sperm.Further analyses reveal that Ccdc38 knockout causes a decreased level of TEKT3,a protein associated with acrosome biogenesis,in testes and an aberrant distribution of TEKT3 in sperm.We finally show that intracytoplasmic sperm injection overcomes Ccdc38-related infertility.Our study thus reveals a previously unknown role for CCDC38 in acrosome biogenesis and provides additional evidence for the occurrence of acrosomal hypoplasia in MMAF.